1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a computer program product for image processing.
2. Description of the Related Art
In recent years, the increased use of color documents has had an impact on, for example, the printing of documents created by individuals or by business enterprises, the displaying of such documents on computer displays, or the displaying of such documents on web pages available on the Web. In these cases, documents including colored characters or color images are created and then subjected to color printing or color display.
In such color documents, colored characters or color-coding with a plurality of colors is often used while grouping reminder notations or graphs in such a way that the colors on their own express important information.
However, because of the fact that color printing is generally expensive as compared with black-and-white printing, it is often the case that black-and-white printing is preferred due to a cost-cutting perspective.
For that reason, even if color documents are created in which the colors themselves express important information, sometimes the information expressed by the colors is lost.
Usually, in the case of performing black-and-white printing of a color document, the luminance components are extracted from the color information in the color image data and the document is printed in such a way that the luminance components are reproduced.
Hence, even when two different colors are used that have equivalent luminance components, it becomes difficult to distinguish those colors on the printed material. Besides, colors having high luminance are reproduced in a pale manner (because the high luminance makes it difficult to distinguish the color from the white paper). Thus, if coloring is done to emphasize reminders, it has the contrary effect and reminders become rather inconspicuous.
A technology has already been disclosed for preserving the differences in colors in a color document even when the document is subjected to black-and-white printing (see Japanese Patent Application Laid-open No. H10-151830). In that technology, the colors and sizes of the colored characters in the original are recognized and, depending on the colors and sizes, small characters are thickened or the character fonts are altered to fonts having textured characters.
Moreover, in recent years, color image forming apparatuses with two-color-printing mechanism or two-color-printing image forming apparatuses have been developed in which only two colors are usable for printing. During two-color printing, although the color expression remains inferior to color printing, an additional color is expressed other than black-and-white printing. Hence, it becomes possible to perform inexpensive image formation by reducing the consumables.
In the case of two-color printing, usually, color discrimination is performed from color document data and the achromatic portion of the document is printed with a different color than the color used for printing the chromatic portion. In that regard, the recent developments have made it possible for the users to select two different colors to be used for printing.
However, in the conventional technology of black-and-white printing, since character fonts are altered for the purpose of preserving the color differences, the small-sized characters get reproduced as thickly smashed characters thereby causing decline in the character viewability.
Moreover, in the conventional technology of two-color printing, since the achromatic portion and the chromatic portion in color document data are printed with two different colors, the chromatic portion is entirely printed with the same color. As a result, it becomes difficult to distinguish between the actual colors on the printed material. For example, assume that the color document includes characters in black, red, and blue colors. In that case, the red and blue colors are printed in the same color. Consequently, those colors become indistinguishable on the printed material. Thus, for example, instead of classifying the characters into the achromatic portion and the chromatic portion for color discrimination, the settings can be changed where the red color is printed with red color, and a different color than the red color is printed by the colors other than the red color. However, even in the case when color discrimination is done with such settings before performing two-color printing; if the color document includes characters in black, red, and blue colors, then the black and blue colors get reproduced in the same color. Consequently, the color differences present in the color document become indistinguishable on the printed material.
Thus, in the conventional technology, when the input color image data is converted into two-color data before being output, there occurs decline in the character viewability and the color discrimination property.